The invention relates to an autolevelling draw-frame of the textile industry in which drafting of the fiber sliver can be modified in a controlled and/or autolevelled manner. The concept of autolevelling comprises, in this case, control and regulation of drafting. Environmental influences and internal machine influences in an autolevelling draw-frame lead to influences on a plurality of signals and measured values. Recognizing errors in signals, compensating for same and transmitting information to the autolevelling draw-frame to locate errors serves to improve the product quality and to increase the availability of the autolevelling draw-frame.
The known algorithms for autolevelling are created for very specialized tasks. This is, however, the critical situation with conventional autolevelling. The algorithm is tied to fixed precisely defined machine processes and influence magnitudes, i.e. autolevelling is determined by specific computation programs. One disadvantage of this restriction is that environmental factors and those which are attributable to the machine nevertheless influence autolevelling, since they cannot be described sufficiently in the algorithm and therefore cannot sufficiently be compensated for (see EP 412 448).
The fact that such errors can occur in the measured-value signal of the measuring device is significant. A measuring device is normally a mechanical scanning roller. The measuring device can however be based on some other measuring principle. This would have as a consequence that the influence factors described below would take effect to a greater or lesser degree.
The temperature of the scanning rollers supplying a measured-value signal of the thickness of the fiber sliver, for instance, is an influence factor based on the environment. After long stoppage of the draw-frame the scanning rollers have assumed environmental temperature. After the start-up of the draw-frame a period of time which is not defined precisely elapses until the scanning rollers have reached operating temperature (dependant on friction against the fiber sliver), i.e. the diameters of the scanning rollers change in an unknown manner so that the establishment of the measured-value signal is subject to error. This change in the influence parameter temperature on the scanning rollers, until operating temperature is reached, cannot be incorporated precisely into an algorithm and therefore this influence upon the scanning rollers cannot be corrected precisely for autolevelling.
Autolevelling processes have not been able in the past to eliminate these disadvantages effectively.
A factor of a different type which influences the establishment of the measured-value signal is the stoppage time of the fiber sliver until continued processing on the autolevelling draw-frame resumes. During that time, the compressibility of the fiber sliver will change, e.g. due to reoccurrence of rippling, change in humidity, etc., and this leads to a deviation from the measured thickness of the fiber sliver. This situation plays a significant role in the conventional autolevelling processes.
It is a further disadvantage that known autolevelling systems do not locate the cause of a disturbance. For example, when a draw-frame shuts off because the sliver number has been exceeded, it is not possible to know whether medium-wave or long-wave sliver errors were the cause of it. Similarly, disturbances in the transmission between main motor and the pair of main drafting rollers for instance, are not recognized.